The following abbreviations and definitions are herewith defined, where at least some of the abbreviations are referred to within the following description of the prior art and the present invention.    3GPP Third Generation Partnership Project    BCCH Broadcast Control Channel    BSS Base Station Subsystem    E-UTRA Evolved Universal Terrestrial Radio Access    E-UTRAN Evolved Universal Terrestrial Radio Access Network    FDD Frequency Division Duplex    GERAN GSM EDGE Radio Access Network    GSM Global System for Mobile communications    PLMN Public Land Mobile Network    MOCN Multi Operator Core Network    MS Mobile Station    RAT Radio Access Technology    TDD Time Division Duplex    UE User Equipment    UTRA UMTS Terrestrial Radio Access    UTRAN UMTS Terrestrial Radio Access Network
Legacy mobile station (e.g., non-supporting UE): A mobile station that does not support network sharing in the sense that it ignores broadcast system information that is specific for network sharing for 3GPP (E)-UTRAN and GERAN and is limited to becoming registered with the common PLMN indicated by the serving network. The term “network sharing non-supporting UE” may also be used to describe the legacy mobile station (non-supporting UE).
Supporting mobile station (e.g., supporting UE): A mobile station that supports network sharing in the sense that it is able to select a core network operator as the serving operator within a shared network and is therefore not limited to becoming registered with the common PLMN indicated by the serving network. The term “network sharing supporting UE” may also be used to describe the supporting mobile station (supporting UE).
PLMN: A Public Land Mobile Network is a network that is established and operated by an administration or by a recognized operating agency for the specific purpose of providing land mobile telecommunications services to the public. The PLMN is identified by the Mobile Country Code (MCC) and the Mobile Network Code (MNC). Each operator providing mobile services has their own PLMN. PLMNs interconnect with other PLMNs and Public Switched Telephone Networks (PSTN) for telephone communications or with Internet service providers for data and internet access of which links are defined as interconnect links between providers.
PLMN'S RATs: The Radio Access Technologies (RATs) that a given PLMN provides as a part of the service to the public, e.g., GSM, UTRA or E-UTRA.
SI12quater's cells-frequencies: UTRAN's cell and frequency information and/or E-UTRAN's frequencies can be provided in the SI2quater messages that a mobile station uses for idle mode cell (re)selection
SI2ter's frequencies: UTRAN frequencies in the SI2ter messages that a mobile station uses for idle mode cell (re)selection.
Common PLMN: when network sharing is in use within a given cell, the Common PLMN refers to the PLMN of the GERAN network 100 which is identified by the PLMN ID broadcast in the SYSTEM INFORMATION TYPE 3 and SYSTEM INFORMATION TYPE 4 messages (as part of the Location Area Identification). See sub-clauses 9.1.35, 9.1.3 in 3GPP TS 44.018 V11.1.0 (May 2012). Also, see 3GPP TS 23.251 V.11.2.0 (June 2012), and 3GPP TS 24.008 V11.3.0 (June 2012). The contents of these documents are incorporated by reference herein.
Equivalent PLMN: A legacy mobile station can become registered for a GERAN network when it determines that the common PLMN thereof is equivalent to a PLMN it is programmed to consider as a preferred PLMN. As such, different non-supporting mobile stations may become registered for the common PLMN of a given GERAN network (i.e. they all have the same registered PLMN when served by the same GERAN network) while having different preferred PLMNs wherein any non-supporting mobile station may not consider their particular preferred PLMN(s) as being equivalent to the preferred PLMN(s) of other non-supporting mobile stations served by the same GERAN network.
Network sharing for supporting mobile stations is a feature for which there is an ongoing work item within 3GPP Release 11 which allows operators to share deployments costs. FIG. 1 (PRIOR ART) is a basic diagram that illustrates one plausible network sharing scenario where multiple operators share a GERAN radio access network 100 while at the same time each operator has their own dedicated E-UTRAN/UTRAN radio access network 1021, 1022, 1023, 1024 and 1025 for which there is a corresponding unique PLMN value. Each dedicated E-UTRAN/UTRAN radio access network 1021, 1022, 1023, 1024 and 1025 is respectively referred to herein as PLMN 1021, 1022, 1023, 1024 and 1025 and each of these has one or more corresponding (e)NodeBs 1031a, 1031b, 1031c, 1032a, 1032b, 1032c, 1033a, 1033b, 1033c, 1034a, 1034b, 1034c, 1035a, 1035b, and 1035c. In this example, each PLMN 1021, 1022, 1023, 1024 and 1025 is shown as having three (e)NodeBs but they could have any number of (e)NodeBs. Further, each (e)NodeB 1031a, 1031b, 1031c, 1032a, 1032b, 1032c, 1033a, 1033b, 1033c, 1034a, 1034b, 1034c, and 1035a, 1035b, 1035c is shown respectively supporting two cells 1031a1, 1031a2, 1031b1, 1031b2, 1031c1, 1031c2, 1032a1, 1032a2, 1032b1, 1032b2, 1032c1, 1032c2, 1033a1, 1033a2, 1033b1, 1033b2, 1033c1, 1033c2, 1034a1, 1034a2, 1034b1, 1034b2, 1034c1, 1034c2, 1035a1, 1035a2, 1035b1, 1035b2, 1035c1, and 1035c2. However, it should be appreciated that each (e)NodeB 1031a, 1031b, 1031c, 1032a, 1032b, 1032c, 1033a, 1033b, 1033c, 1034a, 1034b, 1034c, and 1035a, 1035b, 1035c can support any number of cells and that they do not have to support the same number of cells.
Today, in the current GERAN network 100, the BSS 104 broadcasts UTRAN/E-UTRAN neighbor cell information and associated thresholds in system information messages 106a and 106b (e.g., SI2quater message 106a and SI2ter message 106b—where the SI2quater message 106a supports both UTRAN and E-UTRAN related information (e.g., UTRAN's cells-frequencies, E-UTRAN's frequencies, thresholds) and the SI2ter message 106b only supports UTRAN related information (e.g., UTRAN's frequencies, thresholds) for both supporting mobile stations 1081, 1082 and 1083 (only three shown) and legacy mobile stations 1101, 1102, 1103, 1104, and 1105 (only five shown). In particular, the BSS 104 broadcasts UTRAN/E-UTRAN neighbor cell information and associated thresholds in SI2quater message 106a. Or, the BSS 104 broadcasts UTRAN/E-UTRAN neighbor cell information and associated thresholds in pairs of SI2quater message 106a and SI2ter message 106b. The BSS 104 also broadcasts a SI3 message 113 which indicates the BSS 104's support for network sharing. In addition, the BSS 104 broadcasts specific network sharing information in the SI22 message 115.
The supporting mobile stations 1081, 1082 and 1083 will each select one of the broadcasted PLMNs 1021, 1022, 1023, 1024 or 1025 identified within the SI22 message(s) 115 when performing cell reselection from the GERAN network 100. Then, in order to ensure that the supporting mobile stations 1081, 1082 and 1083 each have PLMN specific mobility to other RATs it is necessary to provide the supporting mobile stations 1081, 1082 and 1083 with system information to identify frequencies, cells, or combination of both in other RATs which are associated with their respective preferred PLMNs where each supporting mobile station 1081, 1082 and 1083 is programmed with information that identifies one or more of PLMN 1021, 1022, 1023, 1024 or 1025 as a preferred PLMN. To accomplish this, the BSS 104 broadcasts the SI2quater message 106a and SI2ter message 106b to provide this system information (e.g., SI2quater message 106a includes cells-frequencies and SI2ter message 106b includes frequencies) for up to 5 PLMNs to the supporting mobile stations 1081, 1082 and 1083. However, the introduction of network sharing which includes the requirement of the BSS 104 broadcasting the SI2quater/SI2ter messages 106a and 106b has at least one shortcoming associated with the legacy mobile stations 1101, 1102, 1103, 1104, and 1105 that needs to be addressed.
A main shortcoming of the BSS 104 broadcasting SI2quater/SI2ter messages 106a and 106b is that the behavior of the legacy mobile stations 1101, 1102, 1103, 1104, and 1105 is unspecified after they receive the SI2quater/SI2ter messages 106a and 106b as will be discussed in detail after describing some of the basic standardized capabilities of the legacy mobile stations 1101, 1102, 1103, 1104, and 1105. First, when it comes to providing UTRAN information, the 3G Cell Reselection list held by the legacy mobile stations 1101, 1102, 1103, 1104, and 1105 has a limitation of 96 cells (frequency+scrambling code) and eight frequencies on their own as specified in the aforementioned 3GPP TS 44.018. A similar limitation also applies to the E-UTRAN information were a limitation of eight frequencies is specified in the aforementioned 3GPP TS 44.018.
Moreover, the legacy mobile stations 1101, 1102, 1103, 1104, and 1105 have minimum monitoring capabilities which are specified in sub-clause 6.6.4 of 3GG TS 45.008 V11.1.0 (May 2012) (the contents of which are incorporated by reference herein). Per this standard, the legacy mobile station's 1101, 1102, 1103, 1104, and 1105 minimum capabilities include monitoring three frequencies from each of the RATs and mode (FDD or TDD) or a maximum of 64 UTRAN cells. In addition, it is also stated in 3GPP 44.018 that the legacy mobile station's 1101, 1102, 1103, 1104, and 1105 behavior is not specified if the number of frequencies-cells exceeds their monitoring capabilities. Hence, a worst case scenario interpretation based on the above is that some legacy mobile stations 1101, 1102, 1103, 1104, and 1105 may only read the first three frequencies provided within the SI2quater/SI2ter messages 106a and 106b per RAT and mode and all will assume that each of these frequencies supports a preferred PLMN and therefore potentially ignore the remaining information (frequencies) provided within the SI2quater/SI2ter messages 106a and 106b which may provide frequency information corresponding to their preferred PLMNs (actually in some implementations some legacy mobile stations 1101, 1102, 1103, 1104, and 1105 may malfunction completely). In other words, it is unclear how legacy mobile stations 1101, 1102, 1103, 1104, and 1105 will function when the number of cells-frequencies/frequencies in the SI2quater/SI2ter messages 106a and 106b is used to their full information bearing potential. This is especially worrisome when network sharing is supported since in this case most of the frequencies included in the SI2quater/SI2ter messages 106a and 106b may not be associated with a PLMN that any given legacy mobile station 1101, 1102, 1103, 1104, and 1105 considers to be a preferred PLMN. As a result, there is an obvious risk that the legacy mobile station 1101, 1102, 1103, 1104, and 1105 will start monitoring UTRAN/E-UTRAN cells which belong to a “wrong” PLMN 1021, 1022, 1023, 1024 or 1025. To illustrate this problem, the legacy mobile station 1101 which is registered with the common PLMN in the GERAN network 100 while having a preferred PLMN consisting of PLMN 1021 may unknowingly monitor UTRAN/E-UTRAN cells associated with one or more other PLMNs 1022, 1023, 1024 or 1025 to which it has no mobility (i.e. any attempt to acquire service on a PLMN that is not a preferred PLMN can result in the mobile station 1101 experiencing service denial). If the legacy mobile station 1101 starts monitoring UTRAN/E-UTRAN cells which belong to a “wrong” PLMN 1021, 1022, 1023, 1024 or 1025 and eventually determines that one of the monitored cells/frequencies is good enough from a signal strength perspective it may try to select a cell associated with PLMN 1022, 1023, 1024 or 1025 to which is has no access (i.e. no mobility) and eventually will fall back to the GERAN radio access network 100. In other words, any attempt to reselect to such a cell associated with PLMN 1022, 1023, 1024 or 1025 will result in the legacy mobile station 1101 eventually determining that the PLMN supported therein is not one of the legacy mobile station's preferred PLMNs (or an equivalent PLMN of the legacy mobile station's preferred PLMNs). Further, the legacy mobile station 1101 during this time may be unreachable for pages. Hence, there is a need to address these problems and other problems associated with the current network sharing scheme. This need and other needs have been satisfied by the present invention.